Pneumatic hand grinding tool

ABSTRACT

A pneumatic hand grinding tool has a supporting plate and a compressed-air pipe to be connected to a source of compressed air for driving the supporting plate. The supporting plate has a flat surface to which an abrasive sheet is to be attached by suction. For this purpose the supporting plate has ducts leading into the flat surface, which are connected to an ejector unit that forms a source of suction. The ejector unit is arranged on the tool and has members which connect the ejector unit to the compressed-air pipe.

[0001] The present invention relates to a pneumatic hand grinding tool, which has a supporting plate and a compressed-air pipe to be connected to a source of compressed air for driving the supporting plate, the supporting plate having a flat surface to which an abrasive sheet is to be attached.

[0002] In order to fasten an abrasive sheet, by which is here meant a piece of abrasive paper, an abrasive cloth or the like, to a supporting plate, today adhesive abrasive sheets are generally used, which have an adhesive surface that is made to abut against the flat surface of the supporting plate. Such abrasive sheets are relatively expensive and are also difficult to handle because of the adhesive surface which is sensitive to dust and dirt. Besides, they have a limited shelf life and are temperature-sensitive.

[0003] It is also known to use so-called Velcro strips for attaching an abrasive sheet to a supporting plate. An efficient attachment of the abrasive sheet is then obtained, but abrasive sheets for such an attachment are very expensive. Such abrasive sheets do not allow the user to change the format of the abrasive sheet or make dust extracting holes.

[0004] Finally, it is also known to attach an abrasive sheet to a supporting plate by suction of the abrasive sheet to the flat surface of the supporting plate. For such a supporting plate use can be made of ordinary abrasive sheets, i.e. abrasive sheets which have not been treated in a specific way, for instance been provided with an adhesive layer or Velcro strips. Then quick and easy changes of abrasive sheets may take place.

[0005] With a view to attaching the abrasive sheet by suction to the supporting plate, the supporting plate has ducts leading into the flat surface which are connected to a source of suction. In the known tools in which the abrasive sheet is attached by suction to the supporting plate, a source of suction which is disposed outside the tool is used. In a pneumatic hand grinding tool of this sort, it is thus necessary, on the one hand, to connect the tool by means of a compressed-air pipe to a source of compressed air for driving the supporting plate and, on the other, to connect the ducts of the supporting plate to the source of suction by means of a suction pipe. This complicates the use of the tool and limits the use to such locations where, in addition to a source of compressed air, also a source of suction is available.

[0006] The object of the present invention is therefore to provide a pneumatic hand grinding tool, in which the abrasive sheet is attached by suction to the supporting plate and the use of which is not limited to such locations where, apart from a source of compressed air, also a source of suction is available.

[0007] This object is achieved by means of a pneumatic hand grinding tool, which has a supporting plate and a compressed-air pipe to be connected to a source of compressed-air for driving the supporting plate, the supporting plate having a flat surface to which an abrasive sheet is to be attached by suction, and the supporting plate having for this purpose ducts leading into the flat surface, which are connected to a source of suction, the tool according to the present invention being characterised in that the ducts are connected to an ejector unit forming the source of suction, the ejector unit being arranged on the tool and having means for connecting the ejector unit to the compressed-air pipe.

[0008] In a preferred embodiment, the ejector unit comprises at least two ejectors, which are connected to at least two separate duct systems comprising the ducts connected to the respective ejectors. The flat surface of the supporting plate is conveniently, with the aid of sealing means, divided into sections which are separated from each other and associated with the respective duct systems.

[0009] The invention will now be described in more detail with reference to the accompanying drawings, in which

[0010]FIG. 1 is a cross-sectional view of a hand grinding tool according to the present invention,

[0011]FIG. 2 is an exploded view and shows parts included in the tool according to FIG. 1 in cross-section,

[0012]FIG. 3 shows an ejector unit arranged in the tool, in the direction of arrow III in FIG. 2,

[0013]FIG. 4 shows a vacuum distributor arranged in the tool, in the direction of arrow IV in FIG. 2,

[0014]FIG. 5 shows a supporting disc arranged in the tool, in the direction of arrow V in FIG. 2, and

[0015]FIG. 6 shows the supporting disc in the direction of arrow VI in FIG. 2.

[0016] The hand grinding tool shown in FIG. 1 has a casing 1 and a handle part 2 connected thereto. The tool is pneumatically operated and has a compressed-air motor 3 which by means of a compressed-air pipe 4 extending through the handle part 2 is connected to a source of compressed air (not shown).

[0017] The output shaft 5 of the motor 3 has a threaded, axial bore at its end facing away from the motor. A bolt 6, whose head 7 forms a spacing means and is non-rotatably connected to a circular metal washer 8 that will be described in more detail below, is screwed into the end bore of the shaft 5 in order to rotate with the shaft together with the washer S. The bolt head 7 also has a threaded axial bore 9 at its free end, and the centre hole of the washer 8 is located opposite this bore 9. A bolt 10 is screwed into the bore 9 of the bolt head 7 to rotate with the bolt head, and thus with the motor shaft 5.

[0018] A circular supporting disc 11, which consists of a supporting sheet 12 of metal and a rubber sheet 13 provided with knobs which are directed outwards (downwards in FIG. 1), is non-rotatably connected to the bolt 10. The supporting disc 11 thus rotates with the bolt 10, and consequently with the bolt 6 and the motor shaft 5. The supporting disc 11 has a circumferential rubber skirt 14 which forms an outer, peripheral sealing lip.

[0019] The supporting disc 11 of the tool is eccentrically rotated, and for this purpose the tool has an eccentric device 15 which is of prior-art type and therefore is not further described here.

[0020] The tool has an ejector unit 16 which is non-rotatably connected to the casing 1 and consists of a collar 17 and four ejectors 18 attached to its circumference. The ejectors 18 are evenly distributed along the circumference of the collar 17. The ejectors 18 are of conventional type and have a through compressed-air passage 19 and a transverse duct 20 connected thereto, which leads into the radially inwards directed surface of the ejector 18. The compressed-air passage 19 is at its one end connected to the source of compressed air through the compressed-air pipe 4 and an ejector pipe 21 which is connected thereto.

[0021] The collar 17 has in its outwards (downwards in FIGS. 1 and 2) directed surface, two circular, concentric grooves or ducts 22 and 23. The grooves 22 and 23 are sealed radially inwards, between them and radially outwards by means of three sealing rings 24, 25 and 26. The sealing rings 24, 25 and 26 abut against the inwardly directed surface of the washer 8. The collar 17 has, opposite each ejector 18, a duct 27, 28, which constitutes a radial extension of the duct 20 of the ejector. The duct 27 communicates with the inner annular groove 22, whereas the duct 28, which is shorter than the duct 27, communicates with the outer annular groove 23. Two of the four ejectors 18 are in this way connected to the inner annular groove 22, while the two others are connected to the outer annular groove 23.

[0022] The ejector unit 16 has four arms 29 which protrude radially from the collar 17 and which at their free end have a pin 30. Each pin 30 is introduced into a corresponding hole 31 in a fixing lug 32 which is formed on the casing 1. A compression spring 33 is arranged on each pin 30 to press the collar 17 against the washer 8 rotating with the shaft 5.

[0023] The washer 8 has two groups of passages 34, 35. In one of the groups, the passages 34 are distributed along an inner circle which has the same radius as the inner annular groove 22 of the collar 17, and in the other group, the passages 35 are distributed along an outer circle, which has the same radius as the outer annular groove 23 of the collar 17. The passages 34 of the washer 8 are thus located opposite the inner annular groove 22 of the collar 17, while its passages 35 are located opposite the outer annular groove 23 of the collar 17. The passages 34, on the one hand, and the passages 35, on the other, are sealed radially inwards, between them and radially outwards by means of three sealing rings 36, 37 and 38. The sealing rings 36, 37 and 38 abut against the inwardly directed surface of the supporting sheet 12.

[0024] The supporting sheet 12 has two groups of through holes 39, 40. In one of the groups, the holes 39 are distributed along an inner circle, which has the same radius as the inner annular groove 22 of the collar 17, and in the other group, the holes 40 are distributed along an outer circle, which has the same radius as the outer annular groove 23 of the collar 17.

[0025] The rubber sheet 13 has, in its inwardly directed surface, an inner circular centre recess 41, which extends a distance into the sheet. A plurality of holes 42, which lead into the flat outer surface, defined by the knobs, of the sheet 13 communicate with the recess 41. The holes 42 are distributed along a circle which is concentric with the shaft 5. The rubber sheet 13 has also in its inwardly directed surface an outer circular groove 43 and, extending radially outwards therefrom, a plurality of grooves 44, which terminate a distance from the circumference of the sheet 13. A hole 45, which leads into the outer surface of the sheet 13, communicates with each groove 44 at the radially outer end thereof. The rubber sheet 13 has a narrow, circular, continuous portion 46 which forms a sealing ring between the openings of the holes 42, on the one hand, and the openings of the holes 45, on the other.

[0026] As will be evident from the above, the radially inner holes 42, which lead into the flat outer surface of the sheet 13, communicate with two of the ejectors 18 through the recess 41, the passages 34, the groove 22 and the ducts 27. The two ejectors 18 form a source of suction for the duct system which is formed by the holes 42, the recess 41, the passages 34, the groove 22 and the ducts 27. As will further be evident, the radially outer holes 45, which lead into the flat outer surface of the sheet 13, communicate with the other two ejectors 18 through the grooves 44, the groove 43, the passages 35, the groove 23 and the ducts 28. The two last-mentioned ejectors 18 form a source of suction for the duct system which is formed by the holes 45, the grooves 44, the groove 43, the passages 35, the groove 23 and the ducts 28. The two duct systems are separated from each other by means of the sealing rings 25, 37 and 46. The duct system 27, 22, 34, 41, 42 is sealed radially inwards by means of the sealing rings 24 and 36, and the duct system 28, 23, 35, 43, 44, 45 is sealed radially outwards by means of the sealing rings 26 and 38 as well as the sealing lip which is formed by the rubber skirt 14.

[0027] A valve 47 is arranged in the compressed-air pipe 4. The valve 47 is by means of a switch (not shown) adjustable from a first position, in which it stops the supply of compressed air to the motor 3 as well as to the ejectors 18, to a second position, in which it still stops the supply of compressed air to the motor 3 but keeps the connection 21 between the compressed-air pipe 4 and the ejectors 18 open, and via the second position to a third position, in which it allows supply of compressed air to the ejectors 18 as well as to the motor 3. Naturally, the valve 47 is by means of the switch also adjustable from the third position to the second position and via the latter to the first position.

[0028] When the valve 47 is in its second position, a suction effect at the flat surface of the supporting disc 11 is thus produced via the two separate duct systems 27, 22, 34, 41, 42 and 28, 23, 35, 43, 44, 45. By this suction effect, an abrasive sheet 48 is attached to the supporting disc 11. Subsequently, the valve 47 is adjusted to its third position, the motor 3 being supplied with compressed air and driving the supporting disc 11 and the abrasive sheet 48 attached thereto. 

1. A pneumatic hand grinding tool, which has a supporting plate (11) and a compressed-air pipe (4) to be connected to a source of compressed air for driving the supporting plate, the supporting plate (11) having a flat surface to which an abrasive sheet (48) is to be attached by suction, and the supporting plate (11) having for this purpose ducts (41, 42, 43, 44, 45) leading into the flat surface, which are connected to a source of suction (18), characterised in that the ducts (41, 42, 43, 44, 45) are connected to an ejector unit (16) forming the source of suction, the ejector unit being arranged on the tool and having means (21, 47) for connecting the ejector unit to the compressed-air pipe (4) with a view to providing the attachment by suction.
 2. A tool according to claim 1 , characterised in that the ejector unit (16) comprises at least two ejectors (18), which are connected to at least two separate duct systems (27, 22, 34, 41, 42 and 28, 23, 35, 43, 44, 45) comprising the ducts (41, 42 and 43, 44, 45) connected to the respective ejectors (18).
 3. A tool according to claim 2 , characterised in that the flat surface of the supporting plate (11) is divided, with the aid of sealing means (46), into sections which are separated from each other and associated with the respective duct systems (27, 22, 34, 41, 42 and 28, 23, 35, 43, 44, 45).
 4. Supporting plate for use in a pneumatic hand grinding tool according to claim 2 , characterised in that the flat surface of the supporting plate is divided, with the aid of sealing means (46), into sections which are separated from each other and associated with the respective duct systems (27, 22, 34, 41, 42 and 28, 23, 35, 43, 44, 45). 